The present invention relates to the beneficiation of phosphate-containing ore by froth flotation. More particularly, the invention relates to a beneficiation method wherein sodium silicate (Na.sub.2 SiO.sub.3) is added to the final stage of conditioning and preparation for anionic froth flotation separation of phosphate-containing ores.
Phosphate-containing ores can be beneficiated by froth flotation separation. Typically, the ore is comminuted and classified according to particle size. Extremely fine material, for example, -150 mesh, contains primarily clay slimes and is usually discarded. Coarse fractions may be sold, further classified by particle size, or beneficiated by froth flotation separation.
Froth flotation separates the feed slurry into two streams; the froth, also called the float, which is removed from the surface of the flotation cell, and the underflow, or tailings, which are removed from the bottom of the flotation cell with the majority of the fluid. Subsequently, each stream may be further treated to purify it or to recover valuable compounds.
The impurities in the phosphate-containing ore are not only silicas. Dolomite and various minerals and metallic impurities are often present in varying quantities, as are many other impurities. Various techniques of froth flotation separation are known in the art, depending upon the identity of the impurities and whether it is desired to recover the phosphate values, i.e., the phosphate-containing concentrate, in the float or in the underflow. For example, compare the methods taught in U.S. Pat. Nos. 2,914,173 and 4,364,824.
Prior to entering the flotation machines, the phosphate-containing ore slurry is typically conditioned or reagentized, i.e., it is treated with various chemicals to increase the efficiency of the separation. Chemicals which are anionic are attracted to the phosphate fraction while the gangue, particularly, siliceous material, attracts cationic reagents. Other chemicals, such as modifiers, conditioning agents, and the like, are selected based on the plant operator's needs.
When an anionic agent is utilized in froth flotation of phosphate-containing ores, the concentrated phosphate is the froth. One of the expedients known to those who practice the art is to add sodium silicate, also known as waterglass, to the pre-flotation conditioning step. The sodium silicate acts as a silica depressant, a dispersant, or a pH adjuster, depending upon the identity of the other anionic agents. However, neither the value of selecting the proper timing for the addition of the sodium silicate nor the froth modifying ability of sodium silicate have heretofore been appreciated.
It is an object of this invention to provide a method for concentrating the phosphate-containing fraction of phosphate-containing ores by froth flotation separation.
It is a further object of this invention to provide a method of beneficiating phosphate-containing ores wherein sodium silicate is added to the final stages of conditioning before an anionic froth flotation separation is attempted.